microbiology

Microorganisms are unicellular organisms (capable of existence as single cells), too small to be seen with the naked eye. Among all forms of life on the earth, microorganisms predominate in numbers of species and in biomass, but their occurrence is generally underappreciated because of their small size and the need for a microscope to see individual cells. Although a light microscope is generally required to visualize a single microbial cell, microbial colonies and communities can readily be observed in nature. As discussed below, viruses are noncellular entities and cannot be considered microorganisms. Viruses and cellular microorganisms are considered microbes.